Oxidation and Reduction Reactions | Chemical Reactions | Chemistry

After reading this article you will learn about the oxidation and reduction reactions of substances.

A chemical reaction can be defined as a change in which a substance (or substances) is changed into one or more new substances. In redox reactions both reduction and the oxida­tion processes go on side-by-side.

The oxidation and reduction reactions can be explained in three different ways:

(a) On the basis of oxygen transfer:

Oxidation is a gain of oxygen while reduction is loss of oxygen.

For example:

(b) In terms of hydrogen transfer:

Oxidation is loss of hydrogen and reduction is gain of hydrogen.  

For example, ethanol can be oxidized to ethyl acetate,  

(c) In terms of electron transfer:

Oxidation is loss of electrons and reduction is gain of electrons.

For example: 

Reaction of Nicotinamide Adenine Dinucleotide (NAD):

Nicotinamide Adenine Dinucleotide functions as an electron acceptor in catabolic path­ways. The nicotinamide ring of NAD⁺, which is derived from the vitamin niacin, accepts 2 e^– and one H⁺ (a hydride) in going to the reduced state, as NAD⁺ becomes NADH. NADP⁺ / NADPH is similar, except for an additional phosphate esterified to a hydroxyl group on the adenosine ribose. NADPH functions as an electron donor in synthetic pathways. NAD⁺ is a coenzyme that reversibly binds to enzymes (Fig. 3.36).

The electron transfer reaction may be summarized as:

NAD⁺ + 2 é + H⁺ –> NADH also be written as NAD⁺ + 2 é + 2H⁺ –> NADH + H⁺

Reactions of Flavin Adenine Dinucleotide (FAD):

Flavin Adenine Dinucleotide also functions as an electron acceptor. The portion of FAD that undergoes reduction/oxidation is the dimethylisoalloxazine ring, derived from the vitamin riboflavin. FAD is a prosthetic group that usually remains tightly bound at the active site of an enzyme.

FAD normally accepts 2 é and 2 H⁺ in going to its reduced state (Fig.3.37):

FAD + 2 é + 2 H⁺ —> FADH₂